Abstract
This article presents a brief historical perspective of the F Breathing Circuit, a universal single-limb breathing circuit. The single-limb breathing circuit (tube within a tube configuration) comprises two tubes of sufficient size and compliance, so that either channel enables safe, unrestricted inspiration/expiration at all times in spontaneous and controlled ventilation. The single-limb circuit can function in various modes: as an anesthetic circle circuit as well as a Mapleson-type rebreathing circuit and as a non-rebreathing circuit (e.g., with ICU ventilators) in adult and pediatric patients. Therefore, it qualifies as a universal breathing circuit. Since its first introduction in Japan (1978), which was followed by further modifications and improvements, the circuit was made available in USA and worldwide.